Wrapping and securing loads on pallets

ABSTRACT

A method of and apparatus for wrapping a load on a pallet involving applying a bag of heat-shrinkable polyethylene film over the load and heating the bag in a heating chamber to effect shrinking of the bag. The bag is longer than the combined height of the load and the pallet so as to have mouth end portions which may extend down below the pallet. The pallet is raised to an elevated position in the chamber with the margin of its bottom surface clear for folding the bag mouth end portions thereunder. Hot air is blown downwardly in the chamber all around the bag and directed inwardly under the pallet to an air exit opening at the bottom of the chamber to blow the bag mouth end portions under the pallet for securing the bag to the pallet in place over the load on the pallet.

United States Patent [191 Schwarz [451 Apr. 30, 1974 WRAPPING AND SECURING LOADS ON PALLETS [75] Inventor: Walter Schwarz, Konigshofen im Grabfeld, Germany [73] Assignee: Ferdinand Schwartz GmbH Industrieofenund Maschinenbau KG, Konigshofen im Grabfeld, Germany [22] Filed: Feb. 19, 1971 [21] Appl. No.: 116,936

[30] Foreign Application Priority Data June 10, 1970 Germany 2028482 [52] U.S. Cl. 53/30, 53/184 [51] B65b 53/06 [58] Field of Search 53/30, 184; 34/225 [56] References Cited UNITED STATES PATENTS 3,662,512 5/1972 Zelnick 53/30 3,522,688 8/1970 Kaliwoda et al.... 53/30 3,508,375 4/1970 Myers 53/30 3,640,048 2/1972 Zelnick et a1... 53/30 3,581,458 6/1971 Gustavsson 53/30 2,906,627 9/1959 Payton et al 53/300 X Bell 53/30 Primary Examiner-Roy Lake Assistant Examiner-E. F. Desmond Attorney, Agent, or Firm-Koemig, Senniger, Powers & Leavitt [57] ABSTRACT A method of and apparatus for wrapping a load on a pallet involving applying a bag of heat-shrinkable polyethylene film over the load and heating the bag in a heating chamber to effect shrinking of the bag. The bag is longer than the combined height of the load and the pallet so as to have mouth end portions which may extend down below the pallet. The pallet is raised to an elevated position in the chamber with the margin of its bottom surface clear for folding the bag mouth end portions thereunder. Hot air is blown downwardly in the chamber all around the bag and directed inwardly under the pallet to an air exit opening at the bottom of the chamber to blow the bag mouth end portions under the pallet for securing the bag to the pallet in place over the load on the pallet.

17 Claims, 9 Drawing Figures llR PATENTED 3 0 I974 KIO FIGBB ISI K4 I49 BACKGROUND OF THE INVENTION This invention relates to the wrapping and securing of loads on pallets, and more particularly to a method of and apparatus for shrink wrapping in plastic of loads on pallets.

The invention is especially concerned with the wrapping of a load on a pallet by applying a bag of a heatshrinkable plastic film, e.g., heat-shrinkable polyethylene, over the load on the pallet, and effecting shrinking of the bag on theload by heating it in a shrink tunnel. This mode of wrapping the load on the pallet has been widely practiced, but has presented difficulties, particularly when the bag is heated by hot air, on account of billowing of the bag and uneven shrinkage of the lower end of the bag, also on account of the absence of any securement of the bag to the pallet for stabilization of the load on the pallet, unless additional operations, such as stapling of the bag to the pallet, orstrapping of the load on the pallet are carried out for such securement to hold the enwrapped load on the pallet.

SUMMARY OF THE INVENTION The principal object of this invention is the provision of a method of and apparatus for wrapping a load on a pallet, wherein a bag of heat-shrinkable plastic, e.g., heat-shrinkable polyethylene, is applied over the load and shrunk on the load, and further wherein the bag is firmly secured to the pallet over the load to stabilize the load on the pallet without any specialsecuring operations, and without use of any separate fastening means.

In general, the method involves the application over the load on a pallet of a wrapper (e.g., abag) of a heatshrinkable plastic film (e.g., heat-shrinkable polyethylene), the wrapper having lower end portions adapted to extend downwardly below the pallet. The pallet, with the wrapper in place on the load on the pallet, is disposed in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder. Air is caused to flow inwardly under the pallet to blow the lower end portions of the wrapper under the said margin of the bottom surface of the pallet, first heating and shrinking saidlower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet and further heating the remaining portions of the wrapper to a temperature to effect shrinking of the wrapper on the load. The apparatus involves means for so positioning the pallet, and means for causing the stated flow of air and the heating. Other objects and features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

FIG. 1 is a side elevation of apparatus made in accordance with this invention, with parts broken away;

FIG. 2 is a plan of FIG. 1 in section on line 22 of FIG. 1;

FIG. 3 is an enlarged longitudinal section on line 3-3 of FIG. 2;

FIG. 4 is an enlarged transverse section on line4-4 of FIG. 1;

FIG. 5 is an end view of the apparatus on the scale of FIG. 1;

FIGS. 6 and 7 are detail views of a lift of the apparatus showing it in its lowered retracted position (FIG. 6) and its raised position (FIG. 7); and

FIGS. 8A and 8B are wiring diagrams.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, an apparatus made in accordance with this invention for carrying out the method of the invention is shown to comprise a heating chamber 1 in the form of a so-called shrink tunnel having a bottom generally designated 3, sides each generally designated 5, a top generally designated 7, and being open at its ends as indicated at 9 and '1 1. Roll curtains 9c and 11c are provided for closing the open ends 9 and 11 of the chamber 1. At 13 is generally indicated an endless chain conveyor for conveying pallets P each with a load L thereon and a wrapper B applied over the load into the chamber 1 for heating of the wrapper, and then conveying the pallet with the enwrapped load out of the chamber. As herein illustrated, the wrapper B is a bag of a heat-sealable and heat-shrinkable plastic film, such as a heat-shrinkable polyethylene. The length of the bag, as applied over the load L on the pallet, is greater than the overall height of the pallet and the load. The girth of the bag is somewhat greater than the girth of the load L and the girth (circumference) of the pallet so that the bag may be readily applied over the load and the pallet.

The chamber 1 is of double-walled construction, its bottom having a horizontal lower panel 15 and an upper inside panel or false floor 17, its sides having thermally insulated outside panels 19 and inside panels 21, and its top having a lower inside panel or ceiling 23 and an upper outside thermally insulated panel 25. The inside panels 21 of the sides of the chamber merge with the upper panel 17 of the bottom via curved fillets 27, and with the lower panel 23 of the chamber top 7 via curved fillets 29. At the ends. of the chamber are insulated end walls 31, these having the openings 9 and 11 therein. The inside panel 23 of the top of the chamber has a circular central opening 33 constituting an air inlet for a centrifugal air impeller 35 on the lower end of shaft 37 of an electric motor MB. This motor is mounted on top of chamber l-with shaft 37 extending vertically downward through the upper panel 25 of the top of the chamber and through the opening 33. Immediately below the impeller 35 is a deflector 39 of rectangular shape in plan having a downwardly extending curved flange 40 all around its periphery acting in conjunction with the inside panel 23 of the top of the chamber and the curved fillets 29 to provide a passage 41 for flow of air from the impeller 35 radially outwardly all around the impeller and thence downwardly on the inside of the inner side panels 21 of the sides 5 of the chamber 1 and on the inside of the curtains 9c and when these are lowered to close the end openings 9 and 11 of the chamber.

Air is adapted to exit from the chamber 1 via a rectangular central opening 43 in the inside upper panel or 3 false floor 17 of the bottom 3 of the chamber, and to return to the impeller via the space 45 between the bottom panels and 17, the spaces 47 between the panels 19 and 21 of the sides of the chamber and the space 49 between the panels 23 and 25 at the top of the chamber. Thus, these Spaces 45, 47 and 49 constitute return passages for return flow of air from the air exit opening 43 in the false floor 17 of the chamber to the air inlet 33 for the impeller or blower 35. The air returning to the blower for being blown downward in the chamber is adapted to be heated by means of a gas burner 51 having a perforated combustion tube 53 extending through: the insulated panel 19 at one side of the chamber substantially across the upper space 49 for delivering the hot exhaust gases from the burner directly into the air for heating it. The term air as used herein may thus include the hot exhaust gases from the burner. A blower for venting the space 49 is indicated at 55 in FIG; 1. This may be omitted'if the space 49 may be vented directly to a flue where building conditions permit. It will be understood that an oil burner may be used'instead of a gas burner; as a matter of fact, the air may be heated by means of electrical resistance heaters (located in spaces 47, for example) instead of by means of a burner. i

The above-described construction is such that the hot air output of the impeller 35 is delivered radially outward in all directions from the impeller, flows downwardly in the chamber in a relatively high velocity stream or curtain immediately adjacent the inside faces of the inside side panels 21 and the inside facesof the closed curtains 9c and 110; the stream then turns inward (assisted by fillets 27) and flows over the false floor panel 17 to the opening 43, through which it exits from the interior of the chamber to the space 45 and returns to the impeller via spaces 47and 49.

The curtains 9c and 110, which may be asbestos curtains, for example, are rolled up on curtain rods 9r and 1 1r adapted to be driven in one direction and the other for unrolling the curtains and for rolling them up via a single reversible electric motor MD and suitable drives such as indicated at 5 7 and 59 from the motor to the curtain rods. The latter are journalled in side members such as indicated at 61 on top of the top 25 of the chamber. The curtains extend down from the curtain rods at the ends of the'chamber l with their side edges guided in suitable guides such as indicated at 63 at opposite sides of the end openings 9 and 11 of the chamber.

The conveyor 13, as shown herein, is a triple-chain conveyor comprising three parallel channel-section members each designated 65 extending longitudinally of the apparatus supported above the level of the floor F with their webs vertical on transverse channel-section members 67. A chain 69 is trained around sprockets 71 on shafts 73 and 75 at the ends of the channel members 65, each chain having a horizontal upper working reach 69u travelling over and supported by the upper flange of the respective channel member 65, and a lower return reachtravelling over the lower flange of the respective channel member 65. The channel members 65 and chains 69 extend through openings 77 therefor in the bottom portions of the end walls 31 of the chamber 1 with the upper flanges of the channels generally at the level of the floor panel 17 of the chamber, this panel having longitudinal slots 79 therein for passage of the upper reaches 69u of the chains with these reaches at an elevation above the level of the floor panel 17 via the slots 79. The two outer chains 69 travel at opposite sides of the air exit'opening 43 in the floor panel 17, and the central chain 69 travels on the longitudinal center line of the opening 43 from end-to-end of the latter. At MC is indicated an electricmotor for driving shaft to drive the conveyor 13 via a speed reducer 83, with the upper reaches 69u of chains 69 travelling from left to right as viewed in FIGS. 1 and 2 for conveying loaded pallets P from a first station at 18 (the loading station) to a second station 2S (the wrapping station) at the entrance end 9 of the chamber 1 thence to a third station 3S (the lift or heating station) in the chamber over the air exit opening 43 in the floor panel 17, thence to a fourth station 45 (the cooling station) outside the chamber at its exit end, and thence to a fifth station 5S (the unloading station) at the forward end of upper reaches 69a of the chains 69. The arrangement is such that a loaded pallet may be delivered to (loaded on) the chains at 1S by a fork lift truck, indexed to 25 where a bag B is applied, indexed to 3S for heating in thechamber, indexed to 4S for cooling outsidethe chamber, and then indexed to SS for removal (unloading) by a fork lift truck. The chains 69 bear the weight of the pallet and the load on the pallet by their engagement with the upper flanges of channels 65.

When a loaded pallet P, with a bag B over the load, stops in the chamber 1 at station 38, the pallet is lifted up off the chains 69u and held for a timed interval in lifted position by a lift generally designated operable via the air exit opening 43 in floor panel 17 of the chamber. This lift 85 comprises a pair of horizontal platforms each designated 87, each of these platforms being supported at. its ends on toggle linkages 89 and 91 for movement between a lowered position below the upper reaches 69u of the chains.(FIGS. 1, 5 and 6) and a raised position above the upper reaches 69u of the chains (FIGS. 3, 4 and 7). One platform 87 is located on one side and the other is located on the other side of the central channel 65 and the central chain 69. Each toggle linkage comprises a pair of links 93 and 95 pin-connected together at 97 at the knee of the toggle, each link 95 being pin-connected 99 to a member 101 secured to channels 65 and each link 93 having a pin connection at 103 with the respective platform 87. The knees of the two toggle linkages for each platform are interconnected by links 105, and the toggles are adapted to be operated by a hydraulic cylinder 107 having one end pivoted as indicated at 109'below the central channel 65 and having a piston rod 11 I extending through its other end connected via a piston rod extension 1 13 with a sleeve on a shaft 1 17 extending between two channel-section legs 119 on links 93 of the two front toggles 89. Shaft 117 carries rollers 121 between the flanges of the channel-section legs 119. The arrangement is suchthat on extension of the piston rod 111 from the cylinder 107, the toggles are folded for lowering of the platforms 87 (FIG. 6) and on retraction of the piston rod into the cylinder the toggles are unfolded to extend vertically and lift the platforms 87 (FIG. 7).

At 125 in FIG. 6 is indicated a valve for controlling the operation of the hydraulic lift cylinder 107. This valve has an up solenoid U adapted when energized to set the valve for supplying hydraulic fluid from a source of pressurized fluid to the right end of cylinder 107 (as viewed in FIG. 6) and to ventits left end of fluid for retraction of the piston rod 1 11, 113 to raise the lift, and a down solenoid D adapted when energized to set the valve-for supplying hydraulic fluid to the left end of the cylinder and to vent its right end for extending the piston'rod 111, 113 to lower the lift.

At S1 in FIG. 8B is indicated a main switch for turning the apparatus on and off. At S2 in FIGS. 3 and 8B is indicated a switch operable by one of the curtains (e.g., curtain 9c as shown) when it is closed, and at S3 in FIGS. 3 and 8B is indicated a switch operable by the curtain 9c when it is opened. At S4 in FIGS. 3, 4 and 8B is indicated a chain drive control switch operable by each one of a-series of lugs such as indicated at 127 on one of the chains 69 (e.g., the central chain) upon indexing of the chains to carry a pallet from station to station. For this purpose, lugs 127 are spaced along the chain at intervals corresponding to the station spacing and switch S4 is mounted in a fixed position for actuation thereof by a lug each time a pallet reaches station 3S (or 2S, 4S or 5S). At S5 in FIGS. 6 and 8B is indicated a switch operable by the piston rod 111, 113

when it is extended for downward movement of the lift platforms 87 and reaches its fully extended position. Each of switches S2, S3 and S4 has a normally open set of contacts a and a normally closed set of contacts b. Switch S5 has two sets of normally closed contacts a and b. Contacts S2a are open and S2b are closed when the curtains are up. Contacts S2a close and 82b open when the curtains 9c and 1 10 close (i.e., when they are lowered). Contacts S3a are open and S3b are closed when the curtains are up. Contacts S3a close and S3b open when the curtains are lowered. Contacts S4a close and 34b open when switch S4 is actuated by a lug 127 (i.e., when a pallet reaches station 35). Contacts S4a and b are closed whenthe lift 85 is down.

Referring to FIG. 8A, the blower motor MB is shown as a three-phase AC motor connected across threephase power supply lines L1, L2, L3 in a circuit 131 including normally open contacts K3a of a relay K3. The conveyor drive motor MC is shown as a three-phase motor connected across lines L1, L2, L3 in a circuit 133 including normally open contacts K6a of a relay K6. The reversible curtain drive motor MD is shown as a three-phase motor connected across lines L1, L2 and L3 in a curtain-opening circuit 135 including normally open contacts K8a of a curtain opening relay K8. A curtain-closing motor-reversing circuit 137 including normally open contacts K9a of a curtain-closing relay K9 is connected around contacts R8a, the arrangement being such that when contacts R8a are closed the motor MD is driven in the direction to open (raise) the curtains and when contacts R9a are closed the motor MD is driven in the opposite direction to close (lower) the curtains.

Referring to FIG. 8B, gas burner 51 is shown as connected across electric power supply lines L4 and L5 in series with a normally closed thermostatic switch 139 and normally closed contacts K31; of relay K3 in a line 141. The main switch S1 is shown as connected in'line L5. A shrink timer relay K1 is connected in series with normally open contacts K5a of a relay K5 and contacts S2a of switch S2 in a line 143. The coil of a time delay relay K2 is series-connected with normally open the coil of relay Kl. The coil of relay K3 in seriesconnected with normally closed contacts K4b of relay K4 in a line 147 shunted around the K1 coil and contacts K5a. The coil of relay K4 is series-connected with normally open contacts K4e of relay K4 and normally open contacts KSb of relay K5 in a line 149 across L4 and L5. Normally open contacts Kla of relay K1 are connected in a line 151 in shunt around contacts K4e and K511. The coil of relay K5 is connected in series with contacts S4a of switch S4 in a line 153 across L4 and L5. The coil of relay K6 is seriesconnected with contacts S4]; of switch S4, a of switch S5 and S3b of switch S3 in a line 155 across L4 and L5. Normally open contacts K7a of a relay K7 and normally open contacts K1 1a of a time delay relay K11 are series-connected in a line 157 shunted around contacts 54b and S50. The coil of relay K7 is seriesconnected with normally open contacts K4d and K5c of relays K4 and K5 and contacts 55b of switch S5 in a line 159 shunted around relay coil K6 and contacts K7a and K1 1a. The coil of relay K8 is series-connected with contacts 83a of switch S3, normally closed contacts K9b of a relay K9 and normally open contacts K8b of relay K8 in a line 161 across L4 and L5. Normally open contacts K2a of relay K2 are connected in a line 163 in shunt around contacts K8b. The coil of relay K9 is series-connected with contacts S2b of switch S2, normally closed contacts K8c of relay K8 and normally open contacts K9c of relay K9 in a line 165 across L4 and L5. Normally open contacts K10a of a relay K10 are connectedin a line 167 in shunt around contacts K9c. The coil of relay K10 is seriesconnected with normally open contacts K511 of relay K5 in a line 169 across L4 and L5. The coil of a time delay relay K11 is series-connected with normally open contactsK4e of relay K4 in a line 171 across L4 and L5. A warning lamp 173 is series-connected with normally open contacts K6b of relay K6 in a line 175 across L4 and L5. The lamp is series-connected with contacts K4e via a connection 177 between 171 and 175. The coil of a relay K12 is series-connected with normally open contacts K12a of relay K12 ia line 179 across L4 and L5. Normally open contacts K8d of relay K8 are connected in a line 181 in shunt around contacts K12a. The coil of a relay K13 is seriesconnected with normally open contacts Kl3a of relay K13 in a line 183 across L4 and L5. Normally open contacts K9d of relay K9 are connected in a line 185 in shunt with contacts Kl3a. The coil of a pallet lift timer relay K14 is series-connected with normally open contacts K12b of relay K12 in a line 187 across L4 and L5 and with normally open contacts K13b of relay K13 via a line 189 in shunt around contacts K12b. This relay K14 has normally closed contacts K14a in line 5 between lines 175 and 179. The down solenoid D of valve 125 is series-connected with normally open contacts K12c of relay K12 in a line 191 across L4 and L5 and the up solenoid U of this valve is series-connected with normally open contacts K130 of relay K13 in a line 193 across L4 and L5.

As will appear, with the main switch S1 closed, the apparatus operates automatically in cycles, functioning on each cycle to operate the conveyor 13 to index a loaded pallet P with a bag B shrunk thereon from the cooling station 4S to the unloading station 5S for removal therof, to index a loaded pallet P with a heated bag B thereon from the heating station 3S in chamber 1 to the cooling station 4S, to index a loaded pallet P with a bag B thereon from the wrapping or bagapplying station 2S to station 3S and to index a loaded pallet P from the loading station 1S to the bag-applying station 28 for application of a bag thereto. The conveyor dwells between its successive intervals of operation, with sufficient dwell time for removal of the loaded pallet with bag B cooled and shrunk thereon from the conveyor station S and for loading of a loaded pallet to be shrink-wrapped on the conveyor at station 18, and application of a bag to be loaded pallet at station 28. Also, durin'g each dwell, the pallet at station 38 in chamber 1 is raised off the conveyor by the lift 85, held raised while the bag B thereon is being heated by hot air delivered by the blower 35, and then lowered back down on to the conveyor 13 for the next indexing operation.

Assuming that the curtains 9c and 1 are up, so that contacts 820 and S3a and open and 52b and S3b are closed, when the main switch S1 is closed, relay K6 is energized via contacts S4b, S5a and S3b all closed in line 155. On energization of relay R6, its contacts K6a in motor circuit 133 close to energize the motor MC to drive the endless chanin conveyor 13 in forward direction, i.e., for travel of the upper reaches 69a of chains 69 from left to right as viewed in FIGS. 1 and 2. Its contacts K6b in line 175 close to energize relay K11 and the warning lamp 173.

The conveyor 13 is driven until one of the lugs 127 v on the central chain-69 actuates switch S4, opening its contacts 84b and closing its contacts 54a. Opening of contacts 841; deenergizes relay K6 'to open contacts K6a and deenergize motor MC thereby to stop the conveyor. This effects the indexing of the conveyor tto transport the pallets from station to station, including the transport of a loaded pallet P with a bag B thereon from station 28 to station 38 in the chamber 1.

On closure of contacts S4a, relay K5 is energized, closing its contacts K5a, KSb, K50 and K511 in lines 143, 149, 159 and 169. Closure of contacts K5a, K5b and K50 readies the circuits forrelays K1, K4 and K7, and closure of contacts KSd energizes relay K10 to close contacts Kl0a in line 167. On closure of contacts K10a, relay K9 is energized via contacts S2b (closed at this time), K80 (normally closed) and K10a, and contacts K9a in circuit 137 close, K9b in line 161 open, and K90 in line 165 and K9d in line 185 close. With contacts K80 in line 165 closed, a holding circuit is es- 'tablished for relay K9 (via 521?, K80 and K90). With contacts K9a closed, the curtain drive motor MD is energized for operation in the direction to unwind and close (lower) the curtains 9c and 110. 1

With contacts K9d in line 185 closed, relay K13 is energized, closing its contacts K13a, K13b and K130. Closure of contacts K13a establishes a holding circuit for relay K13. Closure of contacts K130 energizes the up solenoid U of valve 125 to retract the piston rod 111, 113 and raise the lift 85, thereby to lift the pallet at station 38 up off the upper reaches 69a of the chains 69 of conveyor 13. Closure of contacts Kl3b in line 189 energizes relay K14 which-after a time delay (e.g., 6 seconds) opens its contacts Kl4a to deenergize relays K13, K14 and solenoid U thereby stopping the lift 85 in its raised position.

When the curtains 90 and 110 reach their lowered closed position, switch S2 is actuated. Switch S3 has been previously released by the closing of the curtains so that contactsS3a are closed and S3b are open. When switch S2 is actuated, its contacts 52a in line 143 close and it contacts 82b in line 165 open. contacts S21:

deenergizes relay K9 to open contacts K9a and stop the curtain drive motor MD with the curtains in their lowered closed position (FIG. 3). Closing contacts S2a energizes relay K3 (via closed contacts K4b) closing contacts K3a in circuit 131 to start the blower motor MB to drive the blower 35, and also closing contacts K3b in line 141 to start the burner 51. It also energizes shrink timer relay K1 via closed contacts K5a.

When the shrink timer K1 has timed out its time interval (e.g., 20-25 seconds) its contacts Kla in line 151 close, energizing relay K4. The resultant closure of contacts K in line 149 holds relay K4 energized (contacts KSb being closed); the resultant closure of contacts K40 in line 171 energizes relay K11 and the warning lamp 173 (via line 177); the resultant closure of contacts K4a in line 145 energizes relay K2, and the resultant closure of contacts K4d in line 159 readies relay K7. The resultant opening of contacts K4b on line 147 deenergizes relay K3 and hence opens contacts K3a and K3b to deenergize the blower motor MB and the burner 51. After its time delay, relay K2'closes its contacts K201 in line 163, thereby energizing relay K8 (contacts S3a and contacts K912. being closed). Contacts K8b close to hold relay K8 energized. Contacts K8a in circuit 135 close to energize the curtain drive motor MD for operation in the direction to raise (open) the curtains 90 and 110.,Contacts K80 open. Contacts K8d in line 181 close to energize relay K12, closing contacts K12a in line 179 to hold relay K12 energized, closing contacts K12b in line 187 to energize the time delay relay K14, and closingv contacts K120 in line 191 to energize the down solenoid D of valve 125. This results in extension of the piston rod 111, 113 (see FIG. 6) to lower the lift 85, thereby lowering the pallet back down onto the upper reaches 6914 of the chains 69 of conveyor 13 at station 38.

When relay K11 has timed out its time delay interval (e.g., 5 to 6 seconds), it closes its contacts K1 1a in line 157 and readies relay K6 for energization. Switch S2 is released when the curtains start opening, and switch S3 is actuated when the curtains reach their open position. Release of switch S2 results in deenergization of relays K1 and K2 via opening of contacts S2a. Actuation of switch S3 results in deenergization of relay K8 via opening of contacts S3a. This opens contacts K8a in circuit to stop the curtain drive motor MD with the curtains up. Actuation of switch S3 also closes contacts 83b and readies the K6 and K7 circuits. When the lift 85 reaches its down position, it actuates switch S5, closing its contacts 85a in line and closing its contacts 85b in line 159. With SSaand S3b thus closed (and K7a and K1 1a closed as a result of energization of K7 and K11), relay K6 is energized, thus closing contacts K6a to start the conveyor motor MC and initiate another cycle.

From the above it will appear that after a bag G has been applied over the load L on a pallet P at station 28, the conveyor 13 is indexed (moved forward one station interval) to transport the loaded pallet P with the bag B thereon to the heating station 38 in the heating chamber 1. As previously noted, the bag B is longer than the combined height of the pallet and load so as to have lower end portions (i.e., mouth end portions) such as indicated at B1 in FIGS 1, 6 and 7 adapted to extend downwardly below the pallet P when the pallet is raised off the upper reaches 69a of chains 69 by the lift 85 (see FIG. 7). When the pallet arrives at station 38, the

conveyor 13 stops. The curtains 9c and 110 close, the lift 85 is actuated to raise the pallet, theblower 35 and the burner 51 the set in operation. When the pallet P IS RAISED BY THE LIFT 85, the margin of the bottom surface of the pallet around all four sides of the pallet is cleared for folding of the lower end portions B1 of the bag thereunder. The blower 35 causes a flow of air laterally outwardly in passage 41 toward the inner side panels 21 of chamber 1 and endwise in passage 41 toward the ends of the chamber (closed by the curtain closures 9c and 110), thence downwardly at the sides and ends of the chamber, thence inwardly under the sides and ends of the pallet P (held up by the lift 85), thence down through the exit opening 43, laterally outward via space 45, up through spaces 47 and back to the blower 35 via space 49 and air inlet 33 for the blower.

With the arrangement shown, the air delivered by blower 35, heated by the burner 51, flows at a relatively low velocity and relatively gently downwardly on the outside of all four sides of the bag B, and flows at a relatively high velocity downwardly adjacent the inside side panels 21 and the closed curtains 9c and 11c and then horizontally inwardly from all four sides under the pallet at relatively high velocity. This results in the lower end portions B1 of the bag being blown in (immediately upon the start of hot air circulation) under the margin of the bottom of the pallet at all four sides of the pallet. The bag is heated by the low velocity gently flowing air in contact with the outside of the bag (and by radiation of heat from the chamber walls, which will be relatively hot). The provision for low velocity hot air flow in contact with the bag is highly advantageous because it provides for effective transfer of heat to the bag, without causing whipping and tearing of the plastic material, which becomes soft due to its being heated.

The lower end portions B1 of the bag B are quickly heated to shrink temperature by the high-velocity stream of air flowing inwardly under the pallet, and these infolded portions B1 start to shrink before the main body of the bag starts to shrink, noting that it takes longer to heat the main body of the bag up to shrink temperature by the low-velocity gentle stream of air in contact with the main body of the bag (as distinguished from the high-velocity air flow rushing past the infolded lower end portions B1). Portions Bl may also start to become heat-sealed together where they contact one another underneath the pallet adjacent its four corners. The quick shrinkage of the portions B1 under the pallet in effect locks the bag in place over the load on the pallet generally before any shrinkage of the main body of the bag. Consequently, the shrinkage of the main body of the bag takes place with the bottom end of the bag locked to the pallet, enabling the development of the maximum shrink forces in the bag, which results in complete unitization and stabilization of the load. Further, the bottom end of the bag, being locked under the pallet, and the utilization of the shrink forces of the bag creates a force greater than any aerodynamic forces thereby minimizing billowing and uneven shrinking of the bag.

When the heating (by the flow of hot air and radiation from the chamber walls) of the plastic material of the main body of the bag to a temperature sufficient to effect its shrinkage has been concluded (determined by the time factor of relay K1), the burner 51 and the blower 35 are turned off, the lift 85 is lowered to lower the pallet P (with the heated bag B thereon), the curtains 9c and 110 are opened, and the conveyor 13 is indexed to transport the pallet from station 38 in the chamber 1 to station 48 outside the chamber, where the bag cools. At the same time, a pallet is moved from 48 to 58 for removal, another pallet is transported to station 35 in the chamber for the next cycle, and a pallet is transported from station 18 to 28 for application of a bag thereto.

When a pallet is lowered by the lift 85 back down onto the upper reaches 69a of chains 69 of conveyor 13, the infolded lower end portions B1 of the bag adjacent the sides of the pallet are pinched down against the two outside chains 69, and this pressurizes portions Bl adjacent the four corners of the pallet to heat-seal them together. At station 48, the bag cools and shrinks taut on the load, and, with its mouth end portions Bl folded and shrunk under the pallet around all four sides of the pallet and heat-sealed together adjacent the corners, the bag is effectively secured to the pallet for securement (stabilization) of the load L on the pallet. It will be observed that this is effected without any separate fasteners, such as staples, or strapping.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be illustrative and not in a limiting sense.

What is claimed is:

1. The method of wrapping and securing a load on a pallet comprising applying over the load'a wrapper of a heat-shrinkable plastic film, the wrapper having lower end portions adapted to extend downwardly below the pallet, positioning the pallet, with the wrapper in place on the load on the pallet, in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, causing a flow of heated air downwardly over the wrapper on the outside of the the pallet, the air flowing inwardly under the pallet blowing the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the said margin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallet generally before any shrinkage of the main body of the wrapper by the downwardly flowing air takes place.

2. The method of claim 1 wherein the wrapper is heated to a temperature sufficient to cause the lower end portions of the wrapper blown under the pallet to become heat-sealed 3. The method of claim 1 wherein the wrapper is a plastic bag applied in inverted position over the load,

the mouth end portions of the bag being blown in by the air under the said margin of the bottom surface of I the pallet.

4. The method of claim 3 wherein the pallet with the bag over the load thereon is elevated to the said operating position, the mouth end. portion of the bag then hanging down below the level of the bottom surface of the pallet before being blown inwardly under the pallet.

5. The method of wrapping and securing a load on a pallet comprising applying over the load a wrapper of a heat-shrinkable plastic film, the wrapper having lower end portions adapted to extend downwardly below the pallet, positioning the pallet, with the wrapper in place on the load on the pallet, in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end'portions of the wrapper thereunder,- causing a flow of heated air downwardly over the wrapper on the outside of the wrapper and changing its direction thence to flow inwardly under the pallet, the air flowing inwardly under the pallet blowing the lower end portions of the wrapper under the said margin of'the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the said margin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallet generally before any shrinkage of the main body of the wrapper by the downwardly flowing air takes place, the wrapper being a plastic bag applied in inverted position over the load, the mouth end portions of the bag being blown in by the air under the said margin of the bottom surface of the pallet, the heating of the bag being effected by heating air and blowing it downwardly in a relatively low velocity stream over the bag and in a relatively high velocity stream outwardly of the low velocity stream and inwardly under the pallet, the pallet with the bag over the load thereon being elevated off a supporting means to the said operating position with the said margin of the bottom surface of the pallet clear for blowing in the mouth end portions of the bag under said margin, said mouth end portions of the bag hanging down below the level of the bottom surface of the pallet when the pallet is elevated off said supporting means, and the pallet being lowered back down onto said supporting means after the blowing in of said mouth end portions and the heating with resultant pressing down of said mouth end portions on said supporting means.

6. Apparatus for wrapping and securing a load on a pallet utilizing-a wrapper of avheat-shrinkable plastic film applied over the load and having lower end portions adapted to extend downwardly below the pallet comprising means for positioning the pallet with the wrapper in placeon the load on the pallet in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, and means for causing a flow of heated air downwardly over the wrapper on the outside of the wrapper and changing its direction thence to flow inwardly under the pallet, said flow-causing means comprising means including a blower for effecting blowing of air downwardly in a relatively low velocity stream over thewrapper and in a relatively high velocity stream outwardly of the low velocity stream and inwardly under the pallet, the air flowing inwardly under thepallet blowing the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure'the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the saidmargin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallet generally before any shrinkage'of the main body of the wrapper by'the downwardly flowing air takes place.

7. Apparatus as set forth in claim 6, comprising a chamber having a bottom with an air exit opening therein, said positioning means comprising a lift for raising the pallet adapted to hold the pallet in position above said air exit opening.

8. Apparatus for wrapping and securing aload on a pallet utilizing a wrapper of a heat-shrinkable plastic film applied over the load and having lower end portions adapted to extend downwardly below the pallet comprising means for positioning the pallet with the wrapper in place on the load on the pallet in an operating position wherein the margin of the bottom surface of the pallet is clear for dispostion of the said lower end portions of the wrapper thereunder, and means for causing a flow of heated air downwardly over the wrapper on the outside of the wrapper and changing its direction thence to flow inwardly under the pallet, the air flowing inwardly under the pallet blowing the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the said margin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallet generally before any shrinkage of the main body of the wrapper by the downwardly flowing air takes place, said air flow means comprising means including a blower for causing said flow of air downwardly over the wrapper and thence inwardly under the pallet, means for heating the air, and a chamber having a bottom with an air exit opening therein, said positioning means being adapted to hold the pallet in position above said air exit opening, siad positioning means comprising a lift movable upwardly via said opening from a lowered retracted position at the bottom of the'chamber to a raised position above said opening.

9. Apparatus as set forth in claim 8 wherein said chamber has at least one access opening, a closure for said opening, and a conveyor for transporting a loaded pallet with a wrapper thereon into position above the lift for being raised thereby to said operating position, and for transporting a pallet after heating of the wrapper out of the chamber.

10. Apparatus as set forth in claim 9 wherein said chamber has an entrance opening at oneend thereof, an exit opening at its other end, closures for said openings, and a conveyorextending endwise through the bottom of the chamber for transporting a loaded pallet with a wrapper thereon from a station outside the entrance end of the chamber to a lift station in the chamber with the pallet above the lift and for transporting a pallet after heating of the wrapper from the lift station to a cooling station outside the exit end of the chamber.

11. Apparatus as set forth in claim having means for indexing the conveyor to transport a pallet from station to station, means for opening the closures for transport of the pallets and closing the closures upon completion of each transport, means for operating the blower and the means for heating the air for a timed interval upon closing of the closure, means for actuating the closure opening means upon completion of said interval, and means for actuating said indexing means upon opening of the closures.

12. Apparatus as set forth in claim 6 comprising a heating chamber having a bottom, sides and a top, the bottom having an upper panel with an air exit opening therein for communication from the chamber to the space below said upper bottom panel, the sides having inside panels providing side air passages extending upwardly from the said space below the said upper bottom panel, the top having an inside lower panel with an air inlet opening therein, an air deflector, below said air inlet opening, a centrifugal air impeller below said inside lower top panel mounted for rotation on a generally vertical axis and postioned to'draw in air through the inlet opening and blow it radially outward in respect to said axis, said air deflector being below said impeller and adapted in conjunction with the inside top panel and the inside side panels to cause the air to flow downwardly 'at the sides and ends of the chamber, said positioning means being adapted to support the pallet in position above said air exit opening.

13. The method of wrapping and securing a load on a pallet comprising applying over the load a wrapper of a heat-shrinkable plastic film, the wrapper having lower end portions adapted to extend downwardly below the pallet, positioning the pallet, with the wrapper in place on the load on the pallet, in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, causing a flow of air inwardly under the pallet to blow the lower end portions of the wrapper under the said margin on the bottom surface of the pallet and heating the wrapper to a temperature such as to effect shrinking of the wrapper on the load including shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the wrapper being a plastic bag applied in inverted position over the load, tee mouth and end portions of the bag being blown in by the air under the said margin of the bottom surface of the pallet, the heating of the bag being effected by heating air and blowing it downwardly in a relatively low velocity stream over the bag and in a relatively high velocity stream outwardly of the low velocity stream and inwardly under the pallet, the mouth end portions of the bag blown under the pallet being heated and shrunk prior to the heating and shrinking of the remaining portions of the bag, and the air being heated to a temperature sufficient to cause the mouth end portions of the bag blown under the pallet to become heat-sealed together as well as shrunk, the pallet with the bag over the load being elevated off a supporting means to the said operating position with the said margin of the bottom surface of the pallet clear for blowing in the mouth end portions of the bag under said margin, said mouth end portions of the bag hanging down below the level of the bottom surface of the pallet when the pallet is elevated off said supporting means, and the pallet being lowered back down onto said supporting means after the blowing in of said mouth end portions and the heating with resultant pressing down of said mouth end portions on said supporting means. l

14. Apparatus for wrapping and securing a load on a pallet utilizing a wrapper of a heat-shrinkable plastic film applied over the load and having lower end portions adapted to extend downwardly below the pallet comprising means for positioning the pallet with the wrapper in place on the load on the pallet in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, and means for causing a flow of air inwardly under the pallet to blow the lower end' portions of the wrapper under the said margin of the bottom surface of the pallet and for heating the wrapper to a temperature such as to effect shrinking of the wrapper on the load including shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, said air flow means comprising means including a blower for causing said flow of air downwardly over the wrapper and thence inwardly under the pallet, means for heating the air, said apparatus comprising a chamber having a bottom with an air exit opening therein, said positioning means being adapted to hold the pallet in position above said air exit opening, and said positioning means comprising a lift movable upwardly via said opening from a lowered retracted position at the bottom of the chamber to a raised positioned above said opening.

15. Apparatus as set forth in claim 14 wherein said chamber has at least one access opening, a closure for said opening, and a conveyor for transporting a loaded pallet with a wrapper thereon into position above'the lift for being raised thereby to said operating position, and for transporting a pallet after heating of the wrapper out of the chamber.

16. Apparatus as set forth in claim 15 wherein said chamber has an entrance opening at one end thereof, an exit opening at its other end, closures for said openings, and a conveyor extending endwise through the bottom of the chamber for transporting a loaded pallet with a wrapper thereon from a station outside the entrance end of the chamber to a lift station in the chamber with the pallet above the lift and for transporting a pallet after heating of the wrapper from the lift station to a cooling station outside the exit end of the chamber.

17. Apparatus as set forth in claim 16 having means for indexing the conveyor to transport a pallet from station to station, means for opening the closures for transport of the pallets and closing the closures upon completion of each transport, means for operating the blower and the means for heating the air for a timed interval upon closing of the closures, means for actuating the closure opening means upon completion of said interval, and means for actuating said indexing means upon opening of the closures. 

1. The method of wrapping and securing a load on a pallet comprising applying over the load a wrapper of a heat-shrinkable plastic film, the wrapper having lower end portions adapted to extend downwardly below the pallet, positioning the pallet, with the wrapper in place on the load on the pallet, in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, causing a flow of heated air downwardly over the wrapper on the outside of the wrapper and changing its direction thence to flow inwardly under the pallet, the air being blown downwardly in a relatively low velocity stream over the wrapper and in a relatively high velocity stream outwardly of the low velocity stream and inwardly under the pallet, the air flowing inwardly under the pallet blowing the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the said margin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallet generally before any shrinkage of the main body of the wrapper by the downwardly flowing air takes place.
 2. The method of claim 1 wherein the wrapper is heated to a temperature sufficient to cause the lower end portions of the wrapper blown under the pallet to become heat-sealed
 3. The method of claim 1 wherein the wrapper is a plastic bag applied in inverted position over the load, the mouth end portions of the bag being blown in by the air under the said margin of the bottom surface of the pallet.
 4. The method of claim 3 wherein the pallet with the bag over the load thereon is elevated to the said operating position, the mouth end portion of the bag then hanging down below the level of the bottom surface of the pallet before being blown inwardly under the pallet.
 5. The method of wrapping and securing a load on a pallet comprising applying over the load a wrapper of a heat-shrinkable plastic film, the wrapper having lower end portions adapted to extend downwardly below the pallet, positioning the pallet, with the wrapper in place on the load on the pallet, in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, causing a flow of heated air downwardly over the wrapper on the outside of the wrapper and changing its direction thence to flow inwardly under the pallet, the air flowing inwardly under the pallet blowing the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the said margin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallet generally before any shrinkage of the main body of the wrapper by the downwardly flowing air takes place, the wrapper being a plastic bag applied in inverted position over the load, the mouth end portions of the bag being blown in by the air under the said margin of the bottom surface of the pallet, the heating of the bag being effected by heating air and blowing it downwardly in a relatively low velocity stream over the bag and in a relatively high velocity stream outwardly of the low velocity stream and inwardly under the pallet, the pallet with the bag over the load thereon being elevated off a supporting means to the said operating position with the said margin of the bottom surface of the pallet clear for blowing in the mouth end portions of the bag under said margin, said mouth end portions of the bag hanging down below the level of the bottom surface of the pallet when the pallet is elevated off said supporting means, and the pallet being lowered back down onto said supporting means after the blowing in of said mouth end portions and the heating with resultant pressing down of said mouth end portions on said supporting means.
 6. Apparatus for wrapping and securing a load on a pallet utilizing a wrapper of a heat-shrinkable plastic film applied over the load and having lower end portions adapted to extend downwardly below the pallet comprising means for positioning the pallet with the wrapper in place on the load on the pallet in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, and means for causing a flow of heated air downwardly over the wrapper on the outside of the wrapper and changing its direction thence to flow inwardly under the pallet, said flow-causing means comprising means including a blower for effecting blowing of air downwardly in a relatively low velocity stream over the wrapper and in a relatively high velocity stream outwardly of the low velocity stream and inwardly under the pallet, the air flowing inwardly under the pallet blowing the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the said margin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallet generally before any shrinkage of the main body of the wrapper by the downwardly flowing air takes place.
 7. Apparatus as set forth in claim 6, comprising a chamber having a bottom with an air exit opening therein, said positioning means comprising a lift for raising the pallet adapted to hold the pallet in position above said air exit opening.
 8. Apparatus for wrapping and securing a load on a pallet utilizing a wrapper of a heat-shrinkable plastic film applied over the load and having lower end portions adapted to extend downwardly below the pallet comprising means for positioning the pallet with the wrapper in place on the load on the pallet in an operating position wherein the margin of the bottom surface of the pallet is clear for dispostion of the said lower end portions of the wrapper thereunder, and means for causing a flow of heated air downwardly over the wrapper on the outside of the wrapper and changing its direction thence to flow inwardly under the pallet, the air flowing inwardly under the pallet blowing the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and effecting heat shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the air flowing downwardly over the wrapper effecting heat shrinking of the wrapper on the load, the shrinkage of the lower end portions of the wrapper under the said margin of the bottom surface of the pallet by said inwardly flowing air locking the wrapper in place over the load on the pallEt generally before any shrinkage of the main body of the wrapper by the downwardly flowing air takes place, said air flow means comprising means including a blower for causing said flow of air downwardly over the wrapper and thence inwardly under the pallet, means for heating the air, and a chamber having a bottom with an air exit opening therein, said positioning means being adapted to hold the pallet in position above said air exit opening, siad positioning means comprising a lift movable upwardly via said opening from a lowered retracted position at the bottom of the chamber to a raised position above said opening.
 9. Apparatus as set forth in claim 8 wherein said chamber has at least one access opening, a closure for said opening, and a conveyor for transporting a loaded pallet with a wrapper thereon into position above the lift for being raised thereby to said operating position, and for transporting a pallet after heating of the wrapper out of the chamber.
 10. Apparatus as set forth in claim 9 wherein said chamber has an entrance opening at one end thereof, an exit opening at its other end, closures for said openings, and a conveyor extending endwise through the bottom of the chamber for transporting a loaded pallet with a wrapper thereon from a station outside the entrance end of the chamber to a lift station in the chamber with the pallet above the lift and for transporting a pallet after heating of the wrapper from the lift station to a cooling station outside the exit end of the chamber.
 11. Apparatus as set forth in claim 10 having means for indexing the conveyor to transport a pallet from station to station, means for opening the closures for transport of the pallets and closing the closures upon completion of each transport, means for operating the blower and the means for heating the air for a timed interval upon closing of the closure, means for actuating the closure opening means upon completion of said interval, and means for actuating said indexing means upon opening of the closures.
 12. Apparatus as set forth in claim 6 comprising a heating chamber having a bottom, sides and a top, the bottom having an upper panel with an air exit opening therein for communication from the chamber to the space below said upper bottom panel, the sides having inside panels providing side air passages extending upwardly from the said space below the said upper bottom panel, the top having an inside lower panel with an air inlet opening therein, an air deflector, below said air inlet opening, a centrifugal air impeller below said inside lower top panel mounted for rotation on a generally vertical axis and postioned to draw in air through the inlet opening and blow it radially outward in respect to said axis, said air deflector being below said impeller and adapted in conjunction with the inside top panel and the inside side panels to cause the air to flow downwardly at the sides and ends of the chamber, said positioning means being adapted to support the pallet in position above said air exit opening.
 13. The method of wrapping and securing a load on a pallet comprising applying over the load a wrapper of a heat-shrinkable plastic film, the wrapper having lower end portions adapted to extend downwardly below the pallet, positioning the pallet, with the wrapper in place on the load on the pallet, in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, causing a flow of air inwardly under the pallet to blow the lower end portions of the wrapper under the said margin on the bottom surface of the pallet and heating the wrapper to a temperature such as to effect shrinking of the wrapper on the load including shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, the wrapper being a plastic bag applied in inverted position over the load, tee mouth and end portions of the bag being blown in by the air under the said margin of the bottom surface of the pallet, the heating of the bag being effected by heating air and blowing it downwardly in a relatively low velocity stream over the bag and in a relatively high velocity stream outwardly of the low velocity stream and inwardly under the pallet, the mouth end portions of the bag blown under the pallet being heated and shrunk prior to the heating and shrinking of the remaining portions of the bag, and the air being heated to a temperature sufficient to cause the mouth end portions of the bag blown under the pallet to become heat-sealed together as well as shrunk, the pallet with the bag over the load being elevated off a supporting means to the said operating position with the said margin of the bottom surface of the pallet clear for blowing in the mouth end portions of the bag under said margin, said mouth end portions of the bag hanging down below the level of the bottom surface of the pallet when the pallet is elevated off said supporting means, and the pallet being lowered back down onto said supporting means after the blowing in of said mouth end portions and the heating with resultant pressing down of said mouth end portions on said supporting means.
 14. Apparatus for wrapping and securing a load on a pallet utilizing a wrapper of a heat-shrinkable plastic film applied over the load and having lower end portions adapted to extend downwardly below the pallet comprising means for positioning the pallet with the wrapper in place on the load on the pallet in an operating position wherein the margin of the bottom surface of the pallet is clear for disposition of the said lower end portions of the wrapper thereunder, and means for causing a flow of air inwardly under the pallet to blow the lower end portions of the wrapper under the said margin of the bottom surface of the pallet and for heating the wrapper to a temperature such as to effect shrinking of the wrapper on the load including shrinking of said lower end portions of the wrapper underneath the pallet to secure the wrapper to the pallet, said air flow means comprising means including a blower for causing said flow of air downwardly over the wrapper and thence inwardly under the pallet, means for heating the air, said apparatus comprising a chamber having a bottom with an air exit opening therein, said positioning means being adapted to hold the pallet in position above said air exit opening, and said positioning means comprising a lift movable upwardly via said opening from a lowered retracted position at the bottom of the chamber to a raised positioned above said opening.
 15. Apparatus as set forth in claim 14 wherein said chamber has at least one access opening, a closure for said opening, and a conveyor for transporting a loaded pallet with a wrapper thereon into position above the lift for being raised thereby to said operating position, and for transporting a pallet after heating of the wrapper out of the chamber.
 16. Apparatus as set forth in claim 15 wherein said chamber has an entrance opening at one end thereof, an exit opening at its other end, closures for said openings, and a conveyor extending endwise through the bottom of the chamber for transporting a loaded pallet with a wrapper thereon from a station outside the entrance end of the chamber to a lift station in the chamber with the pallet above the lift and for transporting a pallet after heating of the wrapper from the lift station to a cooling station outside the exit end of the chamber.
 17. Apparatus as set forth in claim 16 having means for indexing the conveyor to transport a pallet from station to station, means for opening the closures for transport of the pallets and closing the closures upon completion of each transport, means for operating the blower and the means for heating the air for a timed interval upon closing of the closures, means for actuating the closure opening means upon completion of said interval, and means for actuating said indexing means upon opening of the closUres. 